The present invention concerns a heat curing silicone rubber composition which can be used, for example, for a wire harness sealer and connector. In more detail, the present invention concerns a heat curing silicone rubber composition having excellent mold release properties which is suitable for use for molding in a metallic mold having an intricate structure.
It is known that silicone rubber compositions lack in mold release properties. Therefore, the rubber tears when it is removed from the mold, and the mold becomes contaminated during operation over an extended period of time. A method has been formerly proposed as a means to solve this problem in which an internal mold release agent, such as stearic acid, zinc stearate, or calcium stearate is added to the silicone rubber composition (Japanese Kokai Patent Application No. Sho 491974!-124151). However, even in silicone rubber compositions in which an internal mold release agent is added, the mold release properties are not sufficient for obtaining silicone rubber molded products having a protruding structure and having an intricate structure, such as a hollow curved structure. The existing silicone rubber composition is not adequate particularly for the molding of multiple silicone rubber products having such intricate structures by one metallic mold. For example, with a mold designed to yield several hundred products per one shot when molding waterproof seal packing for a wire harness connector, a tremendous amount of time is required to remove the product from the mold with existing silicone rubber compositions. Therefore, poor performance in production efficiency is a factor for an increase in cost.
As a result of a search for a solution for the aforementioned problems, the inventors of the present invention have discovered that a silicone rubber composition to which water is added and mixed has excellent mold release properties, and have described this composition in Japanese Kokai Patent Application No. Hei 71995!-126592. They have further discovered that a silicone rubber composition, which is the composition of the aforementioned Japanese Kokai Patent Application to which a specific compound is added and mixed, has superior mold release properties and have completed the present invention. Specifically, the objective of the present invention is to offer a silicone rubber composition having excellent mold release properties which greatly exceeds the mold release properties of existing silicone rubber compositions.